Conventionally, in the field of an actuator controller system having a multi-degree-of-freedom in rotation, which is used for controlling orientation of a monitoring camera and for a joint mechanism of a robot, there has widely been used an actuator mechanism or a motor system with a configuration in which a plurality of single-degree-of-freedom type motors are serially stacked in multistage. From a viewpoint of a reduction in a size and an enhancement in accuracy, in some cases, there is employed a multi-degree-of-freedom type actuator mechanism or a multi-degree-of-freedom type motor system which has a support system using a gimbal mechanism or a joint mechanism and an actuator system using an electromagnetic motor provided separately form the support system. However, in a conventional actuator mechanism or motor system, the serial multistage stacking structure of the single-degree-of-freedom type motors serves as a basic configuration irrespective of the presence of the gimbal mechanism or the joint mechanism. Therefore, the conventional actuator controller system has a difficulty in simplifying its configuration and in reducing its overall size, which cannot always satisfy the required design.
In consideration of the situations, in recent years, attention has been given to a research and development of a spherical motor using a piezoelectric element. In particular, a piezoelectric motor for actuating a spherical member as a driven member by a frictional force using a piezoelectric unit has been expected as a spherical motor of a next generation having small-size and high accuracy.
As a conventional example of a typical application of a motor of this type, there has been known a digital camera that is configured as described in JP-A-2000-059674. The digital camera is provided with an imaging unit, and the imaging unit has: a unit body; a first support frame for supporting the unit body swingably in a vertical direction; a second supporting member for supporting the unit body rotatably in a horizontal direction; an actuator for rotating the unit body in each of vertical and transverse directions; and a position detector for detecting a rotating position of the unit body. The unit body is formed in a shape of a capsule having both cylindrical ends covered with a semispherical surface, and there is provided an imaging unit having an imaging lens on a center of one of the semispherical surfaces and an imaging element in a rear position from the imaging lens. Furthermore, the actuator is disposed to protrude from an upper position of a short side of the second supporting member, and a tip of the actuator is provided to be in contact with a center of the semispherical surface on a rear side of the unit body.
The actuator has a configuration in which a piezoelectric element such as PZT is placed on four side faces of an elastic member having a shape of a square pole, and furthermore, a lamination type piezoelectric element and an abutting piece are placed on an upper end face. The abutting piece is provided with a projection for abutting on the semispherical surface of the unit body.
The imaging unit is set to a predetermined position in which the imaging lens is not exposed from an opening portion in a camera body in a state in which a main switch of the camera is OFF, and the opening portion is shielded with the unit body so that the protection of the imaging lens and the shading of the imaging element are performed. When the main switch is turned ON, the imaging lens of the imaging unit is exposed from the opening portion so that a direction of an optical axis thereof is automatically set to a predetermined position in a front direction and a photographing operation can be performed. Thus, the imaging unit is controlled to be placed in the shielding position of the opening portion and the exposing position of the imaging lens depending on a change in a state of the main switch.
According to the configuration as described above, the actuator having the piezoelectric element has such a structure that the unit body is directly rotated and actuated in each of the vertical and transverse directions. Therefore, it is possible to eliminate the complexity of the conventional structure having the serial multistage stacking configuration of the single-degree-of-freedom motors, thereby expecting a small-sized and multi-degree-of-freedom actuator mechanism.
A similar configuration is also disclosed in JP-A-3-166081.
However, the gimbal mechanism generally has a shaft misalignment caused by a manufacturing process or an assembly process. In a driven member having a spherical shape, particularly, the processing of a rotating bearing portion is difficult to perform and there is a tendency that the shaft misalignment is apt to be generated. An actuating displacement of the piezoelectric element is very small and a frictional contact state of the driven member and the piezoelectric unit greatly varies by the influence of the shaft misalignment. As a result, the actuator characteristic of the piezoelectric motor becomes unstable in some cases. It is also possible to separately provide a mechanism for absorbing the shaft misalignment of the gimbal mechanism, however, Since the size of the whole device is increased, the mechanism would become unsuitable for an application of an actual product so that a design for reducing a size is hindered.